[BUG] block()/blockFirst()/blockLast() are blocking, which is not supported in thread default-nioEventLoopGroup-1 for BlobClientBase.exists()

[loicmathieu]

Describe the bug

Exception when calling BlobClientBase.exists().

Exception or Stack Trace

java.lang.IllegalStateException: block()/blockFirst()/blockLast() are blocking, which is not supported in thread default-nioEventLoopGroup-1-5
    at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:87)
    at reactor.core.publisher.Mono.block(Mono.java:1779)
    at com.azure.storage.common.implementation.StorageImplUtils.blockWithOptionalTimeout(StorageImplUtils.java:146)
    at com.azure.storage.blob.specialized.BlobClientBase.existsWithResponse(BlobClientBase.java:501)
    at com.azure.storage.blob.specialized.BlobClientBase.exists(BlobClientBase.java:479)

To Reproduce Using the following code in a Micronaut controller with file upload. The error shows up only for files of a certain size (more than 1MB).

Code Snippet

    private boolean exists(String path) {
        try {
            BlobClient blobClient = this.blobContainerClient.getBlobClient(path);
            return blobClient.exists();
        } catch (BlobStorageException e) {
            return false;
        }
    }

Setup (please complete the following information):

• OS: Linux 6.8.0-45-generic #45-Ubuntu SMP PREEMPT_DYNAMIC Fri Aug 30 12:02:04 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
• Library/Libraries: com.azure:azure-storage-blob:12.27.1
• Java version: 21
• Frameworks: Micronaut 4.6.3

Information Checklist Kindly make sure that you have added all the following information above and checkoff the required fields otherwise we will treat the issuer as an incomplete report

• [x] Bug Description Added
• [x] Repro Steps Added
• [x] Setup information Added

[github-actions[bot]]

@ibrahimrabab @ibrandes @kyleknap @seanmcc-msft

[github-actions[bot]]

Thank you for your feedback. Tagging and routing to the team member best able to assist.

[loicmathieu]

I found a workaround but it's not pretty:

• Use the asyncClient
• Dispatch all blocking call to an executor

Something like that:

private final ExecutorService executorService = Executors.newSingleThreadExecutor();

    private <T> T block(Mono<T> mono) {
        try {
            return executorService.submit(() -> mono.blockOptional().orElse(null)).get();
        } catch (InterruptedException | ExecutionException e) {
            throw new RuntimeException(e);
        }
    }

[loicmathieu]

It not only happens for exist() but for any method of the BlobClient.